1. Field of the Invention
This invention relates to a tripod type constant velocity universal joint for interconnecting two shafts to permit them to transmit a driving force in a vehicle such as a motor car.
2. Description of the Prior Art
In general, tripod type constant velocity universal joints are for use in transmitting the driving force in vehicles. In the conventional tripod type constant velocity universal joint, as shown in FIG. 1, solidly secured to one end of a first shaft 1 is an outer shell member 2, to the inner surface of which are arranged radially from the center of said first shaft 1 as driving force transmitting elements three tripod shafts 3, onto each of which a roller 4 is mounted rotatably and axially movably in the direction of each tripod shaft 3.
On the other hand, three race grooves 6 are provided in a tulip portion 5a formed at one end of a second shaft 5 in parallel with the axial line of said second shaft 5. Said race grooves 6 are coupled onto said rollers 4, so that a torque can be transmitted between the first shaft 1 and the second shaft 5 through said rollers 4.
Further, formed in the central portion of a trunnion portion 3a of said tripod shaft 3 is a mounting hole 7, in which are provided a compression spring 8 and a mushroom-shaped member 9, which is urged at its head 9a against the wall surface being of substantially spherical shape in cross-section of an open mouth-shaped recess 5b formed in the tulip portion 5a of the second shaft 5 by a biasing force of said compression spring 8.
Furthermore, a tripod spring 10 is mounted on one end of said second shaft 5, and the central portion of said tripod spring 10 is brought into pressing contact with a spherical portion 3b formed on the trunnion portion 3a of the tripod shaft 3, so that said tripod shaft 3 and the second shaft 5 can be connected to each other with no looseness in the axial direction of said second shaft 5.
Further, a boot 11 is provided for covering from outside a connecting portion between both shafts 1 and 5 over a range from the opening portion of the outer shell member 2 of said first shaft 1 to the intermediate portion of the second shaft 5 through bands 12 and 13 provided at opposite ends of said boot 11, respectively. With grease or oil being poured into a space formed around said connecting portion, said boot 11 can prevent dust from entering said connecting portion from outside and can maintain said connecting portion in well lubricated condition.
To transmit a torque when the first shaft 1 and the second shaft 5 are crossed with each other in the abovedescribed tripod type constant velocity universal joint, such a procedure is to be followed that, while the connection between the first shaft 1, tripod shafts 3 and second shaft 5 is maintained, the rollers 4 are rotated about axes of the tripod shafts 3, moved in the axial directions of the tripod shafts 3, and moved in the longitudinal directions of the race grooves 6 of the second shaft 5, during which the torque is transmitted between the shafts 1 and 5, whereby momentary rotary centers of the first shaft 1 and the second shaft 5 are progressively displaced, so that rotary angular velocities of the shafts 1 and 5 can be made equal to each other.
At this time of torque transmission, the central portion of the tripod spring 10 is brought into relatively slidable contact with the spherical portion 3b of the trunnion portion 3a of the tripod shaft 3. However, when a joint angle of the tripod type constant velocity universal joint is increased as shown in FIG. 2, the value of sliding of the second shaft 5 in the axial direction is increased due to a frictional force caused by sliding between the rollers 4 and the tripod shafts 3 as indicated by an arrow in FIG. 2, whereby a thrust force applied to the compression spring 8 due to the sliding of the second shaft 5 in the axial direction is increased.
Then, if said thrust force becomes larger in value than a preset load of the compression spring 8, the tripod spring 10 and the spherical portion 3b of the tripod shafts 3 are momentarily separated from each other, and vibrations and noises take place when said tripod spring 10 and said spherical portion 3b abut against each other again.
Now, to make the tripod spring 10 and the spherical portion 3b of the tripod shafts 3 to not easily be separated from each other, the preset load of the compression spring 8 should be increased (See FIG. 5), and, to increase said preset load, a spring constant of the compression spring 8 should be increased. However, in such a case, the tripod spring 10 and the spherical portion 3b repeatedly slide with both parts being always urged against each other under a large magnitude of force, thus resulting in increased wear of the tripod spring 10.
Consequently, in the conventional tripod type constant velocity universal joint, the vibrations and noises which take place between the tripod spring 10 and the spherical portion 3b of the tripod shaft 3 have not effectively been prevented when the joint angle is large.